Thermal evaporation apparatus, use and method of depositing a material

ABSTRACT

Thermal evaporation apparatus for depositing of a material on a substrate, comprising material storage means; heating means to generate a vapour of the material in the material storage means; vapour outlet means comprising a vapour receiving pipe having vapour outlet passages, and emission reducing means arranged such that an external surface of the vapour outlet means directed to said substrate exhibits low emission, and wherein the apparatus further comprises pipe heating means in the interior of said vapour outlet means, wherein at least the surfaces of the material storage means, heating means, and emission reducing means and pipe heating means arranged to come into contact with the material vapour are of a corrosion-resistant material. Further a thermal evaporation apparatus for depositing a material on a substrate comprising a vapour outlet means arranged to receive in its interior the vapour of the material heated in a material storage means and having vapour outlet passages, wherein said vapour outlet means basically consist of a corrosion-resistant material and are gastight to such an extent that sufficient dynamic pressure of said material vapour is achievable for homogenous deposition of said material on said substrate. Also the use of the apparatus, and a method of depositing a material onto a substrate by thermal evaporation.

FIELD OF THE INVENTION

The present invention relates to a thermal evaporation apparatus fordeposition of various kinds of thin films on a substrate at a highdeposition rate and more particularly to improvements regarding such anapparatus leading to a higher durability of the thermal evaporationapparatus, especially when aggressive materials, such as Selenium (Se)are deposited.

BACKGROUND OF THE INVENTION

For example, in the process of manufacturing a Cu(In,Ga)(S,Se)₂semiconductor layer of a CIS solar module, the method of thermal vapourdeposition (hereinafter referred to as “TVD”) is well established todeposit Selenium (Se) thin films on large surface substrates.

In industrial production processes for manufacturing devices comprisinga thin film of thermal vapour deposited material several generalrequirements have to be observed. For example, in order to be effective,an industrial manufacturing process requires a sufficiently highdeposition rate which can be achieved when the TVD is performed at hightemperatures. A further requirement relates to durability of theapparatus employed for TVD. The former requirement contradicts thelatter since higher temperatures lead to higher wear and a reduced lifecycle of the apparatus. In addition, higher temperatures increase therisk of contaminations of the material to be deposited by means of TVD,especially when aggressive materials such as Selenium (Se) are to bedeposited. Particularly, in the field of solar cell semiconductor CISthin films such contaminations may cause impurity traps in thesemiconductor deteriorating the performance. Finally, high corrosionattack due to high processing temperatures makes it difficult to achieveconstancy in apparatus performance which is a further requirement ofindustrial manufacturing processes.

DE 100 21 530 C1 describes a vapour source with an elongated vapouroutlet pipe and a heating rod provided coaxially in the interior of thevapour outlet pipe. The vapour source of DE 100 21 530 C1 isspecifically designed for the manufacturing process of CIS thin filmsolar cells. The material to be deposited is heated in two crucibleswhereby a vapour is generated and the vapour is supplied to the heatedvapour outlet pipe comprising outlet openings through which the vapourescapes from the vapour source for being deposited on a substrate. It ismentioned in DE 100 21 530 C1 that several vapour sources can be used ina serial arrangement to deposit different materials in the manufacturingprocess of a CIS solar cell.

EP 1 424 404 A describes a thermal evaporation apparatus comprising anelectrically heated melting crucible in which the material to bedeposited is stored and melted to generate the vapour. The vapour isreceived in a vapour pipe comprising outlet openings allowing the vapourto escape from the vapour pipe. The vapour pipe is surrounded by aheater, and radiation reflectors are arranged in order to direct theheat provided by the heater to the vapour pipe.

There is a need for a thermal evaporation apparatus which is capable ofdepositing any material, including aggressive materials, such asSelenium (Se), at high deposition rates.

There is also a need for a thermal evaporation apparatus which can beoperated at high temperatures up to and above 400° C., and even muchhigher, in order to achieve high deposition rates.

There is further a need for a thermal evaporation apparatus which isresistant to wear even at high temperatures and in the presence ofaggressive materials such as Selenium (Se).

There is a still further need for a thermal evaporation apparatus whichis specifically suited for being employed in the manufacturing processof CIS solar cells.

SUMMARY OF THE INVENTION

The invention provides a thermal evaporation apparatus for depositing amaterial on a substrate, the apparatus comprising

material storage means for receiving the material to be deposited,wherein at least the surfaces of the material storage means arranged tocome into contact with the material vapour are of a corrosion-resistantmaterial, for example a material of the group consisting of but notbeing limited to quartz, fused silica, ceramic, graphite andcarbon-fibre-enforced-carbon (CFC);

heating means for heating the material in the material storage means togenerate a vapour of the material;

vapour outlet means arranged to receive in its interior the vapour ofthe material heated in said material storage means, said vapour outletmeans comprising

a vapour receiving pipe having vapour outlet passages, wherein at leastthe surfaces of the vapour receiving pipe arranged to come into contactwith the material vapour are of a corrosion-resistant material, forexample a material of the group consisting of but not being limited toquartz, fused silica, ceramic, graphite and carbon-fibre-enforced-carbon(CFC), and

emission reducing means arranged such that an external surface of thevapour outlet means directed to said substrate exhibits low emission,wherein at least the surfaces of the emission reducing means arranged tocome into contact with the material vapour are of a corrosion-resistantmaterial, for example a material of the group consisting of but notbeing limited to fused silica and ceramic, and wherein the apparatusfurther comprises

pipe heating means arranged in the interior of said vapour outlet means,preferably being a line shaped pipe heating means extending along or inparallel with a longitudinal axis of said vapour receiving pipe, saidpipe heating means being provided with an outer corrosion-resistantsurface arranged to come into contact with the material vapour and beingformed of a corrosion-resistant material, for example a material of thegroup consisting of but not being limited to quartz, fused silica,ceramic, and graphite.

The above thermal evaporation apparatus is also described in claim 1.Advantageous embodiments are described in the subclaims.

The thermal evaporation apparatus allows to deposit aggressivematerials, such as Selenium (Se), at high deposition rates. Surfaces ofcomponents that come in contact with the vapour are of acorrosion-resistant material.

A particular advantage is achieved by the emission reducing means, whichallows to reduce the thermal emission of the vapour outlet means atleast in a direction towards the substrate, so that heating of substrateby radiation from the vapour outlet means is reduced to an acceptablelevel and that the material reaching the substrate is not re-vaporizedfrom the surface of the substrate, even if the vapour outlet means isoperated at high temperatures such as above 350° C., 400° C., or higherthan 400° C. The apparatus can with advantage be used in themanufacturing process of CIS solar cells, and in particular fordepositing Selenium on a precursor of a CIS thin film. Such a precursorcomprises a sequence of layers of different chemical composition, withconstituents of the CIS layer to be formed. After deposition ofSelenium, the precursor has to undergo thermal processing in order toform the CIS layer. During Selenium deposition, the temperature of thesubstrate with the precursor preferably does not exceed a certainmaximum temperature. The maximum temperature is determined taking thesticking coefficient of Selenium into account, which stickingcoefficient is a measure of the balance between deposition andre-evaporation. A suitable maximum temperature for Selenium depositionis 90 degrees C., preferably 80 degrees C., more preferably 70 degreesC.

The emission reducing means suitably exhibits low emission in that itincludes or is made from a material having a low emissivity. Emissivityof a material is the ratio of energy radiated by the material to theenergy radiated by a black body of the same temperature, and istypically denoted as ε, a dimensionless number between 0 and 1. ε=1 is ablack body. Suitably the emissivity of the emission reducing means is0.6 or less, preferably 0.5 or less, more preferably 0.3 or less. Ofparticular relevance is the emission and emissivity in the direction ofthe substrate during normal operation.

The thermal evaporation apparatus for depositing a material on asubstrate according to another aspect of the invention comprises

material storage means for receiving the material to be deposited, saidmaterial storage means consisting of a corrosion-resistant material, forexample a material of the group consisting of but not being limited toquartz, fused silica, ceramic, graphite and carbon-fibre-enforced-carbon(CFC);

heating means for heating the material in the material storage means togenerate a vapour of the material; and

vapour outlet means arranged to receive in its interior the vapour ofthe material heated in said material storage means and having vapouroutlet passages, wherein said vapour outlet means basically consist of acorrosion-resistant material, for example a material of the groupconsisting of but not being limited to quartz, fused silica, ceramic,graphite and carbon-fibre-enforced-carbon (CFC) and wherein said vapouroutlet means are gastight to such an extent that sufficient dynamicpressure of said material vapour is achievable for homogenous depositionof said material on said substrate.

The above thermal evaporation apparatus is also described in claim 21.Advantageous embodiments are described in the subclaims.

A further advantage of the invention is that the vapour outlet issufficiently gastight for the evaporation material, such as aggressiveSe vapour. This also allows to build up sufficient dynamic pressure forhomogenous deposition of the vapour material.

The invention is further directed to the use of a thermal evaporationapparatus of the invention for depositing a material on a substrate, inparticular wherein the material is Selenium, and more in particularwherein the substrate comprises a precursor or precursor layers of a CISlayer.

The invention moreover provides a method of depositing a material onto asubstrate by thermal evaporation, the method comprising

providing a thermal evaporation apparatus comprising heatable materialstorage means for receiving the material to be deposited; and heatablevapour outlet means arranged to receive in its interior the vapour ofthe material heated in said material storage means and having vapouroutlet passages;

selecting a maximum temperature of the substrate during thermalevaporation of the material;

providing emission reducing means for the vapour outlet means, whichemission reducing means are arranged such that an external surface ofthe vapour outlet means directed to said substrate exhibits emissionthat is low enough such that the substrate will not be heated above themaximum temperature during thermal evaporation of the material; and

operating the thermal evaporation apparatus including heating thematerial storage means and vapour outlet means so as to evaporate anddeposit the material on the substrate.

The maximum temperature is selected taking a parameter related tore-evaporation of the deposited material from the substrate, such as asticking coefficient, into account, and/or taking thermal stability ofthe substrate or part thereof into account.

In a particular embodiment the material is Selenium, and more inparticular the substrate comprises a precursor or precursor layers of aCIS layer in thermal equilibrium, e.g. Cu, In, Ga, and/or binary layerssuch as Cu/Ga or In/Ga. The latter case is to be distinguished from CISlayer formation by co-evaporation of CIS constituents onto a hotsubstrate such as discussed for example in U.S. Pat. No. 7,194,197. Inco-evaporation the substrate is kept at a much higher temperature thanwhen depositing a layer on a CIS precursor, because CIS film formationtakes place simultaneously with deposition. Therefore it is specific forthe deposition on a CIS precursor layer that the thermal energy emittedby the evaporation apparatus towards the typically much colder substrateis an issue. In the method of the invention the substrate thereforepreferably does not comprise a CIS precursor layer.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following embodiments of the invention will be described in moredetail and with reference to the drawings, wherein

FIG. 1 shows a first embodiment of a thermal vapour deposition apparatusaccording to the invention;

FIG. 2 shows a cross-sectional view of the first embodiment of a thermalvapour deposition apparatus according to the invention;

FIG. 2 a shows a perspective view of a first variant of an emissionreducing pipe of the first embodiment of a thermal vapour depositionapparatus according to the invention;

FIG. 2 b shows a perspective view of a second variant of an emissionreducing pipe of the first embodiment of a thermal vapour depositionapparatus according to the invention;

FIG. 3 shows a second embodiment of a thermal vapour depositionapparatus according to the invention;

FIG. 4 shows a cross-sectional view of the second embodiment of athermal vapour deposition apparatus according to the invention;

FIG. 5 shows a cross-sectional view of an alternative arrangement of theemission reducing means of any of the embodiments of a thermal vapourdeposition apparatus according to the invention;

FIG. 6 shows a third embodiment of a thermal vapour deposition apparatusaccording to the invention;

FIG. 7 shows a cross-sectional view of the third embodiment of a thermalvapour deposition apparatus according to the invention; and

FIGS. 8 a to 8 c show different arrangements of the vapour outlet meanswith respect to the material storage means of a thermal vapourdeposition apparatus according to the invention.

Where the same reference numerals are used in different Figures, theyrefer to the same or similar objects.

DETAILED DESCRIPTION OF THE INVENTION

Reference is made to FIG. 1. FIG. 1 shows a first embodiment of athermal vapour deposition apparatus according to the invention allowingthe deposition of a material on a substrate at a high rate. Theapparatus of FIG. 1 comprises material storage means 1, which can forexample be a melting crucible, for receiving the material to be meltedand vaporized. The material storage means 1 is heatable by heating means2, for example an electric heater, for heating the material stored inthe material storage means 1 such that a vapour of the material isgenerated in the interior of the material storage means 1. The materialstorage means 1 can also be referred to as material storage container 1.The heating means 2 can also be referred to as heater 2.

The material storage means 1 comprises corrosion-resistant surfacesbeing arranged to come into contact with the material vapour. Thecorrosion-resistant surfaces can be provided by means of acorrosion-resistant material such as quartz, fused silica, ceramic,graphite or carbon-fibre-enforced-carbon (CFC). These materials are ableto withstand aggressive materials, in particular Se and Se vapour. Asuitable ceramic is Al₂O₃. Clearly, not only the surface but the entirewall or body of the material storage means can be of thecorrosion-resistant material.

The apparatus shown in FIG. 1 further comprises vapour outlet means 3which are arranged with respect to the material storage means 1 suchthat the vapour produced of the material stored in the material storagemeans 1 is received in the interior of the vapour outlet means 3.Preferably, the vapour outlet means 3 have an elongated cylindricalshape.

The vapour outlet means 3 comprise a vapour receiving pipe 4 which hasan opening at one end 4 a, forming an inlet for vapour of the vapouroutlet means and vapour receiving pipe, such that the interior of thevapour receiving pipe 4 is in communication with the interior of thematerial storage means 1 to allow the material vapour to propagate fromthe material storage means 1 into the vapour outlet means 3. Preferably,the vapour receiving pipe 4 has an elongated cylindrical shape. As shownin FIG. 1, the vapour receiving pipe 4 comprises vapour outlet passages4 b allowing the material vapour to escape the vapour outlet means 3 ina direction towards a substrate 5 as indicated in FIG. 1 by means ofgrey triangles.

According to the invention, the vapour receiving pipe 4 comprisescorrosion-resistant surfaces being arranged to come into contact withthe material vapour. The surfaces, or in fact the entire wall or body ofthe vapour outlet means and vapour receiving pipe that are arranged tocome into contact with the material vapour are made ofcorrosion-resistant material. The corrosion-resistant surfaces can beprovided by means of a corrosion resistant material such as quartz,fused silica, ceramic, graphite or carbon-fibre-enforced-carbon (CFC).

The vapour outlet means 3 of the apparatus, according a specific andseparate aspect of the invention, further comprise emission reducingmeans 6, for example an emission reducing pipe 6 as shown in FIG. 1accommodating the vapour receiving pipe 4 in its interior, for reducingthe emission of the vapour outlet means 4 at least in a directiontowards the substrate 5. Due to the provision of said emission reducingmeans 6 the heating of substrate 5 by radiation from the vapour outletmeans 3 is reduced such that the temperature of the substrate can bekept at an acceptable level and that the material reaching the substrateis not re-vaporized from the surface of the substrate. Preferably, theemission reducing means 6 have an elongated cylindrical shape.

The emission reducing means 6 comprises corrosion-resistant surfacesbeing arranged to come into contact with the material vapour. Thecorrosion-resistant surfaces can be provided by means of acorrosion-resistant material such as fused silica, ceramic.

By selecting a combination of materials for the vapour receiving pipe 4and the emission reducing means 6 appropriate for a specificapplication, the vapour receiving pipe 4 and/or the emission reducingmeans 6 contribute to the gastightness of the vapour outlet means 3,however depending on the material selected to different extents. In anycase, the material selection according to this aspect of the inventionis performed such that the vapour receiving pipe 4 and/or the emissionreducing means 6 cause the vapour outlet means 3 to be sufficientlygastight so that the gas pressure required for the material vapour toescape from the vapour outlet means 3 in order to propagate towards andreach the substrate 5 is obtained to a sufficient degree when thematerial is heated in the material storage means 1 of an apparatusaccording to the invention. The gastightness achieved according to aspecific and separate aspect of the invention provides the vapour outletmeans 3 with the capability to build up sufficient dynamic pressure forhomogenous deposition of the vapour material.

The gastightness mentioned above can be observed, for example bycomparing the amount of material vapour escaping through the vapouroutlet passages 4 b to the overall amount of material vapour generatedin the thermal evaporation apparatus according to the invention. In apreferred embodiment, the vapour outlet means is arranged such that 75%or more of the material vapour that is produced in the material storagemeans escape from the vapour outlet means 3 through the vapour outletpassages 4 b. According to the invention, the gastightness can befurther increased such that 90% or more, or even at least 99% of thematerial vapour generated in an apparatus according the invention escapefrom the vapour outlet means 3 through the vapour outlet passages 4 b. Aparticularly suitable material is high-density graphite, and coated CFCis another option.

The emission reducing means 6 are provided with vapour passage throughholes 6 a at locations aligned with the vapour outlet passages 4 b ofthe vapour receiving pipe 4 so that the material vapour escaping fromthe vapour outlet means 3 through the vapour outlet passages 4 b in thevapour receiving pipe 4 can propagate essentially unhindered towards thesubstrate 5. For this purpose, the diameter of the vapour passagethrough holes of the emission reducing means 6 is equal or greater thanthe diameter of the vapour outlet passages 4 b of the vapour receivingpipe 4.

According to the invention, the apparatus shown in FIG. 1 furthercomprises pipe heating means 7, which in the embodiment shown is a lineshaped pipe heating means arranged in the vapour receiving pipe 4 suchthat the longitudinal axes of the line shaped pipe heating means 7 andof the vapour receiving pipe 4 run parallel and preferably coincide. Theline shaped heating means 7 heat the vapour outlet means 3 and preventthe material vapour in the interior of the vapour outlet means 3 tocondensate and/or to form droplets.

In the embodiment shown in FIG. 1, the line shaped pipe heating means 7comprise a heating element 7 a and a heating element bulb (cover) 7 b inwhich the heating element 7 a is arranged. Of the heating element 7 aand the heating element bulb 7 b only the latter has an outer surfacewhich faces the interior of the vapour receiving pipe 4 and which comesinto contact with the material vapour.

According to the invention, the line shaped pipe heating means 7comprise an outer corrosion-resistant surface, for example provided bymeans of the above mentioned heating element bulb 7 b, wherein thecorrosion-resistant surface is provided by means of acorrosion-resistant material such as quartz, fused silica, ceramic andgraphite.

Advantageously, the line shaped heating means 7 is a tungsten halogenideIR heater, i.e. a tungsten halide lamp comprising electrical contacts,e.g. two electrical connectors 7 d, for supplying electric energy tosaid tungsten halide lamp.

FIG. 2 shows a cross-sectional view of the vapour outlet means 3 at lineA-A shown in FIG. 1. It is apparent from FIG. 2 that the emissionreducing means 6 are arranged to surround the vapour receiving pipe 4and that the vapour outlet passages 4 b of the vapour receiving pipe 4and vapour passage through holes 6 a of the emission reducing means 6are arranged to allow the vapour to escape from the interior of thevapour outlet means 3 through said passages, in particular they arealigned. As can be taken from FIG. 2, the vapour receiving pipe 4 andthe emission reducing means 6 preferably have a cylindricalcross-section. It is further apparent that in the shown embodiment ofthe invention the vapour receiving pipe 4, the emission reducing means 6and the line shaped pipe heating means 7 are arranged concentricallywith respect to their longitudinal axes.

In FIG. 2 a the emission reducing pipe 6 as described above is showncomprising individual vapour passage through holes 6 a. It should benoted that instead of the individual vapour passage through holes 6 a asdescribed above the emission reducing means 6 may be provided with anelongated vapour passage slit 6 b, as shown in FIG. 2 b, which isaligned with the vapour outlet passages 4 b of the vapour receiving pipe4.

FIG. 3 shows a second embodiment of a thermal vapour depositionapparatus according to the invention which is similar to the firstembodiment in several aspects. Accordingly, the apparatus shown in FIG.3 comprises material storage means 1 for receiving the material to bemelted and vaporized and heating means 2 for heating the material storedin the material storage means 1. Further, the apparatus according to thesecond embodiment comprises vapour outlet means 3 which are arrangedwith respect to the material storage means 1 such that the vapourproduced of the material stored in the material storage means 1 isreceived in the interior of the vapour outlet means 3. As shown in FIG.3 the vapour outlet means 3 comprise a vapour receiving pipe 4 having anopen end portion 4 a and vapour outlet passages 4 b allowing thematerial vapour to escape the vapour outlet means 3 in a directiontowards a substrate 5. Line shaped pipe heating means 7 are provided inthe vapour outlet means 3 as shown in FIG. 3. For further details of thesecond embodiment of the apparatus according to the invention referenceis made to the above description of the first embodiment.

The second embodiment of the apparatus according to the invention alsocomprises emission reducing means 6 which are, however, provided bymeans of an emission reducing layer 6 on at least some portions of thesurface of the vapour receiving pipe 4. The emission reducing layer 6 isarranged such that the vapour outlet passages 4 b of the vapourreceiving pipe 4 are left open so that the vapour is not hindered fromescaping from the interior of the vapour outlet means 3 in the apparatusaccording to the second embodiment of the invention as shown in FIG. 3.

FIG. 4 is a cross-sectional view of the vapour outlet means 3 at lineA-A shown in FIG. 3. It is apparent from FIG. 4 that in the secondembodiment of the apparatus according to the invention the emissionreducing layer 6 is arranged on the surface of the vapour receiving pipe4 and that the vapour outlet passages 4 b are open for the materialvapour to pass through.

FIG. 5 shows an alternative arrangement of the emission reducing layer 6of the second embodiment. The principle of the alternative arrangementis, however, applicable to the emission reducing means of any embodimentof the invention. As is apparent from FIG. 5, the emission reducinglayer 6 according to the alternative arrangement is provided only on aportion of the surface of the vapour receiving pipe 4 such that thesurface portion of the vapour outlet means 3 facing the substrate 5 iscovered by the emission reducing layer 6.

FIG. 6 shows a third embodiment of the apparatus according to theinvention. The apparatus according to the third embodiment comprises allfeatures of the apparatus according to the first embodiment so thatreference is made to the respective description above. However,according to the third embodiment, the apparatus further comprisesradiation absorbing means 8 which are provided to absorb the heatingradiation emitted by the line shaped pipe heating means 7 and to achievean improved efficiency by keeping the energy in the vapour outlet means3 to heat the material vapour. To achieve the desired increase inefficiency, the absorption rate and in particular absorption coefficientof the radiation absorbing means 8 is higher than the absorption rateand in particular absorption coefficient of the vapour receiving pipe 4,respectively, and preferably exceeds 50%. The radiation absorbing meansis provided in the interior of the vapour outlet means and vapour outletpipe.

The radiation absorbing means 8 are especially advantageous if thematerial of the vapour receiving pipe 4 is transparent to the radiationof the heating means to such an extent that the heating radiationemitted by the heating means of the vapour outlet means, such as lineshaped pipe heating means 7, may substantially pass the vapour receivingpipe 4. For example, if the vapour receiving pipe 4 is manufactured of amaterial such as quartz, the radiation absorbing means are made of amaterial such as CFC, graphite, TiN or SiN are particularlyadvantageous. The radiation absorbing means then absorbs the radiationenergy from the heating means transmits thermal energy by radiatingitself at different wavelengths that can be absorbed by the vapourreceiving pipe, and/or by thermal conduction. Generally, according tothe invention, the radiation absorbing means 8 comprisescorrosion-resistant surfaces being arranged to come into contact withthe material vapour. The corrosion-resistant surfaces can be provided bymeans of a corrosion-resistant material such as ceramic, TiN, SiN,graphite or carbon-fibre-enforced-carbon (CFC).

As shown in FIG. 6, the radiation absorbing means 8 may be provided bymeans of a radiation absorbing pipe 8 which is arranged in the interiorof the vapour receiving pipe 4 of the vapour outlet means 3. Theradiation absorbing pipe 8 may be in extensive contact with the vapourreceiving pipe 4 or may be haltered such that the contact between theradiation absorbing pipe 8 and the vapour receiving pipe 4 only exist atsome determined locations 8 a. Alternatively, the radiation absorbingmeans 8 may be provided by means of a radiation absorbing layer which isprovided on the interior surface of the vapour receiving pipe 4 in anarrangement similar to the emission reducing layer mentioned above. Inany case, the radiation absorbing means 8 comprise vapour passagethrough holes 8 b which are aligned with the vapour outlet passages 4 bof the vapour receiving pipe 4 to allow the vapour to escapesubstantially unhindered from the interior of the vapour outlet means 3of an apparatus according to the invention.

According to an alternative embodiment, the radiation absorbing means 8may be provided by means of a radiation absorbing pipe which is arrangedin the interior of the vapour outlet means 3 in the vicinity of the lineshaped heating means 7 and which receives the line shaped heating meansin its interior, respectively. Further, the radiation absorbing means 8may be provided by means of a radiation absorbing layer on the surfaceof the line-shaped heating means 7, which layer can be a coated layer.According to both alternatives, the radiation absorbing means 8effectively can absorb the short wavelength IR radiation of theline-shaped heating means and send out long wavelength IR radiation(black body radiation). A short wavelength is a wavelength lower than anupper threshold of between 1 and 4 micrometer, such as below 2micrometer.

FIG. 7 shows a cross-sectional view of the vapour outlet means 3 at lineA-A shown in FIG. 6. It is apparent from FIG. 7 that the radiationabsorbing means 8 are arranged to be surrounded by the vapour receivingpipe 4 and that the vapour outlet passages 4 b of the vapour receivingpipe 4 and vapour passage through holes 8 a of the radiation absorbingmeans 8 are arranged to allow the vapour to escape from the interior ofthe vapour outlet means 3 through said passages. As can be taken fromFIG. 7, the radiation absorbing means 8 preferably have a cylindricalcross-section. It is further apparent that in the shown embodiments ofthe invention the vapour receiving pipe 4, the emission reducing means6, the line shaped pipe heating means 7 and the radiation absorbingmeans 8 are arranged concentrically with respect to their longitudinalaxes.

Further, according to an advantageous embodiment of the invention, theapparatus comprises a valve means 9, as shown by dashed lines in FIGS.1, 5 and 6, arranged such that the interior of the vapour outlet means 3can be shut to stop the evaporation through the vapour receiving pipe.

According to the invention, the valve means 9 consist of acorrosion-resistant material such as the materials mentioned above.Further, according to another advantageous embodiment of the invention,the apparatus comprises cooling means (2 a) for fast cooling of thematerial storage means (1) and the material contained therein. Saidcooling means allow for a fast stop of evaporation in case of a machineshut down and maintenance. The coolant can be provided in form of a gasor liquid.

In the embodiments of a thermal evaporation apparatus of the inventiondiscussed so far, the material storage means is arranged to supply saidvapour to an end portion of said vapour receiving pipe of said vapouroutlet means, in particular to a lower end of an upright vapourreceiving pipe.

As shown in FIGS. 8 a to 8 c, which are schematic drawings ofembodiments of the invention, it should be noted that the materialstorage means 1 and the vapour receiving means 3 may be arrangeddifferently from the arrangement shown in FIGS. 1, 5 and 6. As shown inFIG. 8 a the vapour outlet means 3 may be arranged at one side of thematerial storage means 1. As shown in FIG. 8 b the vapour outlet means 3may be bent by any degree, for example by 90°. As shown in FIG. 8 c,second material storage means 1′ and second heating means 2′ may beprovided such that the first material storage means 1 and first heatingmeans 2 are arranged at one end of the vapour outlet means 3 and thesecond material storage means 1′ and the second heating means 2′ arearranged at the respective other end of the vapour outlet means 3. Theposition of the substrate 5 is also indicated in FIGS. 8 a to 8 c. Thus,the second material storage means can be arranged at an end portion ofthe vapour receiving pipe.

Where reference is made to a corrosion resistant object, surface, ormaterial in the description or in the claims, this can in particular bea non-metallic object, surface, or material. A suitablecorrosion-resistant ceramic can be Al₂O₃. A measure for corrosionresistance can be the weight increase of a material surface, such as inmg/cm², in a defined atmosphere of a particular vapour pressure andconstitution. For a selenium evaporator, a maximum weight increase of 5mg/cm²; preferably maximum 1 mg/cm², is considered sufficientlycorrosion resistant after being subjected to a Selenium atmosphere at atemperature between 300 and 600 degrees C. for 10 days. Graphite forexample was found to exhibit less than 1 mg/cm² weight increase. Forcomparison, several steels that were tested exhibited 10-50 mg/cm²weight increase.

1-28. (canceled)
 29. A thermal evaporation apparatus for depositing amaterial on a substrate, the apparatus comprising: material storagemeans for receiving the material to be deposited, wherein at least thesurfaces of the material storage means arranged to come into contactwith vapour of the material to be deposited are constructed of amaterial selected from the group consisting of quartz, fused silica,ceramic, graphite and carbon-fibre-enforced-carbon (CFC); heating meansfor heating the material in the material storage means to generate avapour; vapour outlet means arranged to receive in its interior saidvapour, said vapour outlet means comprising: a vapour receiving pipehaving vapour outlet passages, wherein at least the surfaces of thevapour receiving pipe arranged to come into contact with the vapour areconstructed of a material selected from the group consisting of quartz,fused silica, ceramic, graphite and carbon-fibre-enforced-carbon (CFC),and emission reducing means arranged such that an external surface ofthe vapour outlet means directed to said substrate exhibits emissivityof 0.6 or less, wherein at least the surfaces of the emission reducingmeans arranged to come into contact with the vapour are constructed of amaterial selected from the group consisting of quartz, fused silica,ceramic, graphite and carbon-fibre-enforced-carbon (CFC), and whereinthe apparatus further comprises pipe heating means arranged in theinterior of said vapour outlet means, preferably being a line shapedpipe heating means extending along or in parallel with a longitudinalaxis of said vapour receiving pipe, said pipe heating means beingprovided with an outer corrosion-resistant surface arranged to come intocontact with the material vapour and being formed of a material selectedfrom the group consisting of quartz, fused silica, ceramic, andgraphite.
 30. The thermal evaporation apparatus according to claim 29,wherein said emission reducing means is an emission reducing pipeaccommodating said vapour receiving pipe in its interior, preferablywherein said emission reducing pipe comprises at least one of a vapourpassage through holes or a vapour passage slit, being aligned with saidvapour outlet passages of said vapour receiving pipe.
 31. The thermalevaporation apparatus according to claim 29, wherein said emissionreducing means is an emission reducing layer on an external surface ofsaid vapour receiving pipe, said layer being arranged at least on asurface portion of said vapour receiving pipe facing said substrate. 32.The thermal evaporation apparatus according to claim 29, furthercomprising radiation absorbing means comprising corrosion-resistantsurfaces arranged to come into contact with the vapour, thecorrosion-resistant surfaces being constructed of a material selectedfrom the group consisting of quartz, fused silica, ceramic, graphite andcarbon-fibre-enforced-carbon (CFC), for absorbing radiation emitted bysaid line shaped pipe heating means, wherein said radiation absorbingmeans is one of a radiation absorbing pipe provided in said vapourreceiving pipe or a radiation absorbing layer provided on an interiorsurface of said vapour receiving pipe.
 33. The thermal evaporationapparatus according to claim 29, wherein said pipe heating meanscomprise a heating element and a heating element bulb housing theheating element such that only the surface of the heating element bulbfaces the interior of said vapour receiving pipe.
 34. The thermalevaporation apparatus according to claim 29, further comprising valvemeans arranged to control fluid passage through said vapour receivingpipe, said valve means comprising corrosion-resistant surfaces arrangedto come into contact with the material vapour, the corrosion-resistantsurfaces being constructed of a material selected from the groupconsisting of quartz, fused silica, ceramic, graphite andcarbon-fibre-enforced-carbon (CFC).
 35. The thermal evaporationapparatus according to claim 29, further comprising cooling means forcooling the material storage means.
 36. The thermal evaporationapparatus according to claim 29, wherein the vapour receiving pipeand/or the emission reducing means provide the vapour outlet means withsufficient gastightness such that a desired gas pressure is obtainedwhen the material is heated in the materials storage means.
 37. Athermal evaporation apparatus for depositing a material on a substratecomprising material storage means for receiving the material to bedeposited, said material storage means being constructed of a materialselected from the group consisting of quartz, fused silica, ceramic,graphite and carbon-fibre-enforced-carbon (CFC); heating means forheating the material in the material storage means to generate a vapourof the material; and vapour outlet means arranged to receive in itsinterior the vapour of the material heated in said material storagemeans and having vapour outlet passages, wherein said vapour outletmeans comprises a material selected from the group consisting of quartz,fused silica, ceramic, graphite and carbon-fibre-enforced-carbon (CFC)and wherein said vapour outlet means are gastight to such an extent thatsufficient dynamic pressure of said material vapour is achievable forhomogenous deposition of said material on said substrate, and wherein75% or more of said material vapour exit the vapour outlet means throughsaid vapour outlet passages.
 38. A method comprising the use of thethermal evaporation apparatus of claim 29 for depositing a material on asubstrate.
 39. The method according to claim 38, wherein the material isSelenium.
 40. The method according to claim 38 wherein the steps producea component for use a photovoltaic cell.
 41. A method of depositingSelenium onto a substrate by thermal evaporation, the method comprising:providing a thermal evaporation apparatus comprising: heatable materialstorage means for receiving the material to be deposited; and heatablevapour outlet means arranged to receive in its interior the vapour ofthe material heated in said material storage means and having vapouroutlet passages; selecting a maximum temperature of the substrate duringthermal evaporation of the material; providing emission reducing meansfor the vapour outlet means, which emission reducing means are arrangedsuch that an external surface of the vapour outlet means directed tosaid substrate exhibits emission that is low enough such that thesubstrate will not be heated above the maximum temperature duringthermal evaporation of the material; and operating the thermalevaporation apparatus including heating the material storage means andvapour outlet means so as to evaporate and deposit the material on thesubstrate.
 42. The method according to claim 41, wherein the thermalevaporation apparatus is the apparatus according to any one of claims 1.43. The method according to claim 41 wherein the substrate comprises aCIS precursor layer.